Comparing the Most Efficient Heating Systems
Selecting the most efficient heating system is a major part of the buying decision for a new furnace. During the winter, the energy expenditure for heating represents a substantial portion of the household budget. In most houses, it will be the largest single energy expense. Upgrading to a new system represents an obvious opportunity to exchange an outdated furnace, perhaps hampered by performance issues and years of wear and tear, for the latest technology that delivers maximum energy efficiency and enhanced indoor comfort.
Even if you stay in the home, you don’t get the opportunity to make these decisions very frequently. The average service life of a typical gas-fired furnace, for example, is over 15 years. So buyers are entering into a long-term commitment to whatever unit and efficiency level they select now. All the more reason to make those buying decisions only after you’ve carefully considered the options available to you.
The most efficient heating system for one size home won’t be the best choice for another size, nor will it be suitable for every budget. The length of the heating season also matters, as does local fuel availability. The most commonly utilized fuel for heating is natural gas, making up almost 60 percent of the residential market. This is followed by radiant heating from boilers, heat pumps, electric furnaces and, especially on the East Coast, fuel oil.
The word “efficiency” means different things to different people, depending on the context. Energy efficiency, when applied to HVAC systems, generally refers to the amount of heat or cooling produced by a certain amount of fuel consumed. Due to the laws of physics, not all fuel consumed by any style of heater ever converts directly into useable heat energy. Some amount is invariably lost in the process of combustion. Here are the common efficiency standards that express heating efficiency and allow consumers to compare similar models.
Furnace Efficiency Essentials
- Annual fuel utilization efficiency (AFUE) is the primary standard for rating furnace efficiency. The AFUE rating is prominently displayed on the yellow EnergyGuide sticker affixed to all new furnaces marketed in the U.S.
- AFUE is a percentage that expresses the amount of fuel consumed by the unit that actually converts into usable heat energy, averaged out over a year’s usage, versus the amount lost in the combustion process.
- The higher the AFUE rating, the more efficiently the furnace produces heat and, in theory, the lower your heating costs will be.
Minimum AFUE ratings for furnaces are mandated by the government and have steadily climbed in recent years as energy efficiency has become a national priority. Before the 1990s, furnaces generally produced AFUEs in the 60 range. This means 40 percent or more of the fuel consumed by the furnace was lost in the combustion process and didn’t contribute to the actual generation of heat. Where did it go? In most cases, up the ventilation pipe, along with the hot gases that are byproducts of combustion.
In recent years, the Federal minimum AFUE has been 78. As of January 1, 2015, the national standard will increase to 80. Gas-fired furnaces with an AFUE of 80 to 83 are now considered standard efficiency. However, consumers can also choose to upgrade to high-efficiency furnaces. These units, also known as condensing furnaces, recover some of the energy lost in the exhaust gases and utilize it to produce extra heat.
Currently, high-efficiency ratings begin at an AFUE of 90.
Is More Efficient Better?
All advances in technology come with a caveat, and high-efficiency furnaces are no exception. While these units produce more heat from less fuel, they’re also more technologically advanced than a standard AFUE 80 furnace. This means a steeper upfront purchase cost.
Of course, the substantially reduced energy expenses of high-efficiency operation will begin compensating for that increased sticker price from day one. However, the time span before full payback occurs may be many years in locales with moderate winters where the heating season is comparatively short, such as here in central Georgia.
For many homeowners, the most efficient heating system for their home simply means upgrading from an outmoded older unit to a new, affordable AFUE 80 furnace. This may be the best choice, even when compared to a high-efficiency model, particularly if other home efficiency measures are taken such as sealing air leaks and upgrading insulation.
Electric furnaces generate heat with electric resistance coils that glow red hot as current passes through them. Electric models are also rated by AFUE. However, because there’s no combustion flame involved, and no hot gases exhausted, electric furnaces don’t suffer the combustion losses common to gas-fired furnaces. For this reason, the AFUE of an electric furnace is typically very high, commonly above 95.
However, electric heating costs are actually quite steep compared to a gas-fired furnace. In most areas of the country, electricity is more expensive than gas. Only in locales where gas is scarce and costly will an electric furnace be less expensive to operate than a gas-fired model, despite its higher AFUE.
Moving Heat Around
After the air conditioning process was invented in the early 20th century, it was soon noted that a system that cooled a structure by extracting heat energy from air could also be utilized for heating purposes during winter. The first heat pumps developed in the 1940s proved this concept, and after decades of development, heat pumps have taken their place as an energy-efficient home heating choice that also pulls double duty as an air conditioner. I
In heating mode, a heat pump is basically an air conditioner running in reverse, extracting heat energy from outdoor air at an exterior coil and concentrating it in a compressor cycle. It then transfers the heat indoors to be dispersed via ductwork. Down to around 30 degrees, there’s enough latent heat in cold outdoor air to warm your home.
Heat Pump Efficiency Essentials
- Because there’s no combustion involved, a heat pump suffers none of the inherent combustion losses of a gas-fired furnace. And because the only energy consumed is the electricity to run the compressor and blower fan, they’re also very economical.
- In heating mode, the efficiency of air-source residential heat pumps is rated by the heating system performance factor (HSPF). Like the AFUE for gas-fired furnaces, heat pump HSPF is important consumer information included on the yellow EnergyGuide sticker.
- HSPF represents the unit’s heating performance over one heating system by dividing the total amount of BTUs of heat produced by the unit by the total amount of electricity in watt hours consumed by the unit.
Low Temperature Caveats
In the event of a hard freeze below 28 degrees, most air source heat pumps won’t be able to harvest enough latent heat from outdoor air to warm the home. This cutoff point is dropping steadily as heat pump technology advances.
Some new units can now produce sufficient heat at temperatures in the low 20s. Most standard units, however, must activate supplemental heat to continue to warm the home.
Heat pumps incorporate electric resistance coils inside the indoor air handler to generate additional heat, just like the coils in a standard electric furnace. However, because of the high cost of electricity in most locales, frequent reliance on supplemental heating may offset the cost-saving efficiency of a heat pump. Naturally, this occurs principally in local climates where temperatures routinely drop that low. In the Macon area, low temperatures on the average seldom drop below the mid-30s. Occasional reliance on supplemental heating should be an uncommon occurrence limited to infrequent cold snaps, but nevertheless should be figured into the potential cost of relying on a heat pump.
Radiant heat dispersed through a house by water heated in a boiler is a time-tested method for warming a home. Originally utilized as steam that fed radiators in individual rooms, today radiant heat utilizes hot water circulated from a boiler to hydronic baseboard heaters or into grids of tubing incorporated into the slab or installed beneath the flooring. Hydronic systems warm rooms gently from the floor up, heating people and objects in the room instead of heating the air like a forced-air furnace.
Hydronic Heat Efficiency Essentials
- Hydronic heat efficiency estimates are based on the efficiency of the boiler that heats the water.
- Like a gas-fired or electric furnace, boiler efficiency is expressed by the AFUE, which represents the amount of heat lost from the boiler during the heating process versus the amount actually transferred to the water.
- Current federal minimum AFUE for gas-fired boilers is 82.
- High-efficiency boilers, known as condensing boilers, offer AFUE ratings of at least 85. To qualify for the EnergyStar designation, these models must incorporate electronic ignition that eliminates the pilot light, condensing technology to recover heat energy lost in combustion and sealed combustion that utilizes outdoor air piped directly to the combustion chamber.
To select the most efficient heating system for your central Georgia home, contact Wilson Bryant Air Conditioning.
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